Functions
2.8 Motor Protection
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
172
Example: Motor with the following data:
The following settings are derived from these data:
The following settings are made:
IStart/IMOTnom = 4.9
I MOTOR NOMINAL = 0.6 A
T START MAX = 8.5 s
MAX.WARM STARTS = 2
#COLD-#WARM = 1
For the rotor temperature equilibrium time, (address 4304) a setting time of approx. T Equal = 1 min has
proven to be a good value. The value for the minimum inhibit time T MIN. INHIBIT depends on the motor
manufacturer, or by the user's requirements. It must in any case be higher than 4304 T Equal. In this example,
a value has been chosen that reflects the thermal replica (T MIN. INHIBIT = 6.0 min).
The motor manufacturer's, or the requirements also determine also the extension factor for the time constant
during cool-down, especially with the motor stopped. Where no other specifications are made, the following
settings are recommended: Kτ at STOP = 5 and Kτ at RUNNING = 2.
For a proper functioning, it is also important that the CT values and the current threshold for distinction between
stopped and running motor (address 212 BkrClosed I MIN, recommended setting ≈ 0.1 I
MOT.NOM
) have been
set correctly. An overview of parameters and their default settings is generally given in the setting tables.
Rated Voltage V
Nom
= 6600 V
Nominal current I
Nom
= 126 A
Startup current I
STARTUP
= 624 A
Startup duration T
Start max.
= 8.5 s
Permitted starts with cold motor n
cold
= 3
Permitted starts with warm motor n
warm
= 2
Current transformer 200 A / 1 A
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